Multiple users can view the same image on a conventional display device simultaneously. The properties of a conventional display device are such that viewers can see the same image from different angles with respect to the display (hereafter “Public Mode”). This is effective in applications where many users require the same information from the display—such as, for example, displays of departure information at airports and railway stations. However, there are many applications where it would be desirable for an individual user or multiple users to be able to see angular dependent information from the same display. Example 1—“Dual View”: it would be desirable for a single display located on the dashboard of a motorcar to relay satellite navigation data to the driver while a passenger views a film. Example 2—“Privacy”: a single display user who wishes to view confidential material in a public place and would therefore find it desirable to display the confidential image on-axis only (i.e. for the user's eyes only) and to display a non-confidential image off-axis that could be viewed by 3rd parties. Example 3—“3D Function”: in order to view a 3D image (an image with perceived depth) from a display, a single user requires different images (a “stereoscopic pair”) to be directed to each eye.
GB2405542 describes the use of a parallax optic and a display for creating a directional display. Embodiments within GB2405542 concentrate on realising a Dual View display whereby two independent images are viewable in two different principal directions. The application for in-car use is emphasised and accordingly one image is viewable to the left of the display's normal axis while the second image is viewable to the right of the display's normal axis. By directing the same image to both the left and right views, a normal “public” mode is realised. The main disadvantage of the public mode is that images have only 50% resolution and approximately 50% brightness compared to an identical image panel without the parallax optic attached. This relatively poor public mode performance limits the application of the display mode to relatively niche markets. GB2405542 also mentions that a switchable privacy display may also be realised that enables a public wide view mode and a private narrow view mode. However, GB2405542 does not teach explicitly how to realise a privacy display nor does it describe how to electronically switch between the public wide view mode and a private narrow view mode of said privacy display.
On Sep. 27, 2006, Sharp announced a “Triple View Directional Viewing LCD” (hereafter “Triple View Display”) which offers simultaneous display of three independent images by combining an existing liquid crystal device (LCD) with a parallax optic, as illustrated in FIG. 1 of the accompanying drawings. The display 9x comprises a display device 9b and a parallax optic 2 formed on a substrate 7 and displays the three views such that they are viewable in viewing regions 28. This LCD is capable of the following image functions: a public wide view mode and a Triple View mode. In the Triple View mode, three independent images are displayed that are viewable from different directions, such that one image is viewable substantially on-axis by a viewer 5 while another image is viewable substantially off-axis to the left of the display by a viewer 5b while another image is viewable substantially off-axis to the right of the display by the viewer 5c. The Triple View mode also serves as a privacy mode since an on-axis user 5 can view content that cannot be viewed off-axis. By directing the same image to the left to viewer 5b, centre to viewer 5 and right to viewer 5c, a normal public mode is realised on the Triple View Display. The main disadvantage of the public mode is that images have only 33% resolution and approximately 33% brightness compared to an identical image panel without the parallax optic attached. This relatively poor public mode performance limits the application of the display mode to relatively niche markets. GB2426352 describes a display that can yield a public wide view mode, a private narrow view mode and an autostereoscopic 3D mode. U.S. Ser. No. 11/348,602 describes a display that can yield a public wide view mode, a private narrow view mode, a Dual View mode and an autostereoscopic 3D mode. The main disadvantage of both GB2426352 and U.S. Pat. No. 11/348,602 is that, in order to realise a display with extra image functions, an additional liquid crystal switch cell is required. The extra liquid crystal switch cell increases the relative thickness and weight of the whole display module by approximately 40%. The extra weight and thickness are very undesirable, especially for mobile display products such as mobile phones, laptop personal computers etc. Methods of changing the viewing angle properties of a display panel using additional liquid crystal cells are also described in GB2413394; GB2427033, GB2439961, JP09230377 JP3607272, JP3607286, U.S. Pat. No. 5,825,436 and WO04070451.
A number of technologies exist which describe ways of creating switchable privacy by exploiting the natural viewing angle dependence of liquid crystal displays and include JP09230377, U.S. Pat. No. 5,844,640, US20070040975A1, US20070121047A1, US20060109224, US20040207594 and GB2428152A1, JP1999-11-30783, U.S. Pat. No. 6,646,707, JP 1999-11-30783, US20060267905A1, US20070046881, GB2428101, GB patent application no. 0721255.8. Although all of these methods are advantageous in terms of adding no extra thickness or weight to the existing display panel, they are specific to the use of a liquid crystal display (LCD) mode, and could not (for example) be used to make a switchable privacy organic light emitting diode (OLED) display. U.S. Pat. No. 5,844,640, US20070040975 and US20070121047 disclose techniques for changing the viewing angle properties of a single layer LCD panel. This is achieved for a vertically aligned nematic (VAN) LC mode. These techniques are such that parallax optics are unnecessary. Related prior art in the use of lenses and parallax optics for creating non-switchable privacy displays include: JP2002299039, JP2006236655, U.S. Pat. Nos. 6,809,470, 7,091,652, 6,935,914, WO0133598, WO03007663. A display that does not have the capability of switching between a public wide view mode and a private narrow view mode has an inherent disadvantage over displays that are switchable between the two modes.
A method for switching from public to private mode with no moving parts is to mount a light control film behind the display panel, and to place a diffuser which can be electronically switched on and off between the light control film and the panel. When the diffuser is inactive, the light control film restricts the range of viewing angles and the display is in private mode. When the diffuser is switched on, it causes light travelling at a wide range of angles to pass through the panel and the display is in public mode. It is also possible to mount the light control film in front of the panel and place the switchable diffuser in front of the light control film to achieve the same effect. Switchable privacy devices of these types are described in U.S. Pat. Nos. 5,831,698, 6,211,930 and 5,877,829. They share the disadvantage that the light control film always absorbs a significant fraction of the light incident upon it, whether the display is in public or private mode. The display is therefore inefficient in its use of light. Since the diffuser spreads light through a wide range of angles in the public mode, these displays are also dimmer in public than in private mode, unless the backlight is made brighter to compensate.
An addressing scheme for application to LED and OLED displays is described in U.S. Pat. No. 6,421,033 whereby the use of multiple counter electrodes controls the effective resolution enhancement to an active matrix display without increasing the total number of thin film transistors (TFTs). However, U.S. Pat. No. 6,421,033 does not propose to use the multiple counter electrodes in order to yield a multiple image function display.